/*
* JGrass - Free Open Source Java GIS http://www.jgrass.org
* (C) HydroloGIS - www.hydrologis.com
*
* This library is free software; you can redistribute it and/or modify it under
* the terms of the GNU Library General Public License as published by the Free
* Software Foundation; either version 2 of the License, or (at your option) any
* later version.
*
* This library is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more
* details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; if not, write to the Free Foundation, Inc., 59
* Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package org.jgrasstools.gears.utils.math.interpolation.splines;
import java.util.ArrayList;
import java.util.List;
import com.vividsolutions.jts.geom.Coordinate;
/**
* This is adapted from: http://www.cse.unsw.edu.au/~lambert/splines/Bspline.html
*
* @author Tim Lambert (http://www.cse.unsw.edu.au/~lambert/)
* @author Andrea Antonello (www.hydrologis.com)
*/
public class Bspline extends ControlCurve {
// the basis function for a cubic B spline
double b( int i, double t ) {
switch( i ) {
case -2:
return (((-t + 3) * t - 3) * t + 1) / 6;
case -1:
return (((3 * t - 6) * t) * t + 4) / 6;
case 0:
return (((-3 * t + 3) * t + 3) * t + 1) / 6;
case 1:
return (t * t * t) / 6;
}
return 0; // we only get here if an invalid i is specified
}
// evaluate a point on the B spline
private Coordinate p( int i, double t ) {
double px = 0;
double py = 0;
for( int j = -2; j <= 1; j++ ) {
Coordinate coordinate = pts.get(i + j);
px += b(j, t) * coordinate.x;
py += b(j, t) * coordinate.y;
}
return new Coordinate(px, py);
}
final int STEPS = 12;
public List<Coordinate> getInterpolated() {
List<Coordinate> interpolatedCoordinates = new ArrayList<Coordinate>();
Coordinate q = p(2, 0);
interpolatedCoordinates.add(q);
for( int i = 2; i < pts.size() - 1; i++ ) {
for( int j = 1; j <= STEPS; j++ ) {
q = p(i, j / (double) STEPS);
interpolatedCoordinates.add(q);
}
}
return interpolatedCoordinates;
}
}